Summary of Work:A major focus of this project is to discover the role of the Amyloid Precursor Protein (APP) in the etiology and pathology of Alzheimers Disease (AD). The normal physiological role of this protein is also under investigation. APP is important to study since the processing of APP and the effect of Presenilin (PS) mutations on APP processing bear directly on the increased intracellular production and extracellular deposition of A-beta peptides in senile plaques of AD. The processing of APP also generates secreted forms of the protein which may have neurotrophic properties. Brains of AD patients exhibit selective and massive neuronal loss. In light of recent evidence from our laboratory showing that, in cell culture, over-expression of familial AD mutated forms of APP and PS causes apoptotic cell death, we are interested in examining the mechanisms involved in this cell death. One of the aims of our laboratory is to discover how APP or PS mutations lead to specific neuronal cell loss in AD.Previously we showed that over-expression of mutated forms of APP in stably transfected PC12 cells led to an increased production of intracellular, amyloidogenic C-terminal fragments of APP. This was accompanied by increased apoptotic cell death over several days. We recently showed that over-expression of FAD mutant APP by adenovirus-mediated gene transfer leads to cell death of primary cortical neurons. Increased amounts of carboxyl terminal APP fragments and A-beta peptide were detected intracellularly. The overexpression led to about a four-fold increase in apoptotic cell death over 72 hours as measured by an ELISA method detecting fragmented DNA bound to oligonucleosomes. In addition wild-type APP over-expression caused an increase in cell death suggesting that elevated levels of normal APP may have neurotoxic characteristics. This cell death in primary cortical neurons and by extension, in AD, may result from an imbalance in the generation of neurotoxic and neurotrophic processing products of APP. These products may act within the cell or may have a paracrine effect, being released into the media to affect neighboring cells. These results provide a rationale for targeting particular elements of apoptotic pathways and APP processing for therapeutic intervention in AD. - amyloid, A-beta peptide, aging, neurodegeneration, apoptosis